The composition of the rubber in the tread is a major determinant of the running properties of a tire, in particular of a pneumatic tire. Equally, the rubber mixtures used in hoses, drive belts, and other belts, especially in the locations subject to high mechanical load, are in essence responsible for the stability and durability of these rubber products. Very stringent requirements are therefore placed upon these rubber mixtures for pneumatic tires, hoses, drive belts, and other belts.
Partial or complete replacement of the carbon black filler by silica in rubber mixtures over a number of years has increased the overall level of, for example, the running properties of a tire. However, silica-containing tread mixtures still suffer from the known conflicts of objectives between inversely correlated tire properties: an improvement in wet grip and in dry braking generally continues to be attended by impairment of rolling resistance, of winter properties, and of abrasion performance. These properties are also an important criterion of quality in industrial rubber products, such as hoses, drive belts, and other belts.
A wide variety of approaches have already been used in attempts to resolve the conflicts of objectives: by way of example, a very wide variety of unmodified and modified polymers, plasticizers, and fine-particle fillers have been used for rubber mixtures, and attempts have been made to influence the properties of the vulcanisate by making modifications to the process for producing the mixture. Attempts are also being made to blend various polymers with one another, with the aim of improving the properties of the vulcanisate: an example is U.S. Pat. No. 4,471,093, which aims to resolve the conflict of objectives between rolling resistance and wet grip by disclosing a rubber mixture comprising a rubber blend made of a high-molecular-weight styrene-butadiene rubber with a low-molecular-weight butadiene rubber, and comprising natural rubber as further rubber, and comprising carbon black as sole filler. EP502728B1 in turn describes a rubber mixture which attempts to optimize the conflict of objectives between grip properties and abrasion: to this end, this rubber mixture comprises a blend of a high-molecular-weight styrene-butadiene rubber with a low-molecular-weight styrene-butadiene rubber, and comprises from 60 to 250 phr of carbon black as sole filler. U.S. Pat. No. 5,432,232 discloses rubber mixtures featuring improved abrasion, fracture properties, wet grip, ice grip, and dry grip. The rubber mixture described in U.S. Pat. No. 5,432,232 comprises a blend of a high-molecular-weight branched styrene-butadiene copolymer with a low-molecular-weight butadiene rubber, and comprises carbon black as sole filler component. U.S. Pat. No. 5,959,039 attempts to use a rubber blend of a high-molecular-weight styrene-butadiene rubber with a low-molecular-weight styrene-butadiene rubber to optimize flexibility at low temperatures, and equally to optimize grip properties on ice and snow. The rubber mixtures described in U.S. Pat. No. 5,959,039 comprise carbon black as sole filler component. U.S. Pat. No. 6,114,451 discloses rubber mixtures comprising a rubber blend of a high-molecular-weight butadiene rubber with a low-molecular-weight butadiene rubber, and 45 phr of carbon black as sole filler. This rubber mixture exhibits an improvement in respect of abrasion, of wet grip, and of ice grip.
U.S. Pat. No. 6,437,205 discloses that a rubber blend of a first low-molecular-weight polybutadiene with a second high-molecular-weight polybutadiene can be used to improve fracture properties, snow grip, wet grip, and rolling resistance.
The disclosures mentioned do not discuss, or at least do not adequately discuss, the conflict of objectives between rolling resistance, dry braking, and abrasion. Indeed, some of the rubber mixtures described in those specifications and comprising the respective rubber blends mentioned exhibited disadvantages in rolling resistance performance.